Coaxial switch having a tapered, slotted conductor arm



Sept. 21, 1965 J, MOHENRY 3,208,011

COAXIAL SWITCH HAVING A TAPERED SLOTTED CONDUCTOR ARM Filed Aug. 27, 1962 F'FgT (3 H D CL:

IN VEN TOR. VINCENT J. M HENRY A TTORWE Y United States Patent 3,208,011 COAXIAL SWITCH HAVING A TAPERED, SLOTTED CONDUCTOR ARM Vincent J. McHenry, Farmington, Mich, assignor to The Bendix Corporation, a corporation of Delaware Filed Aug. 27, 1962, Ser. No. 219,481 2 Claims. (Cl. 3337) This invention pertains to a coaxial switch for switching the signal from one coaxial cable to one of two other coaxial cables, depending on the position of the switch, with a minimum of signal distortion.

This invention improves over coaxial switch of the prior art such as illustrated in Patent No. 2,472,274 to Beleskas which shows a switch having a cylindrical arm anchored in one end of a tube with spaced coaxial cables being connected to the other tube end to form a T. The free end of the rod is movable by an electromagnet to contact either one or the other of the center conductors of the coaxial cable. The cylindrical rod of Beleskas is reduced in diameter near the anchored end to permit flexing, and the inner surface of the tube is flared outwardly and has an elliptical cross section to improve impedance matching. The disadvantage of this construction is that the tapered elliptical shape of the tube requires expensive machining operations and the manner of reducing the rod to permit flexing introduces discontinuities.

This invention improves upon the prior art by making unnecessary the expensive flared tube of tapered elliptical cross section and by using a flex joint for the arm which minimizes impedance discontinuities in the arm. This invention accomplishes these purposes by tapering a center arm in a straight sided tube and reducing the diameter of the arm at the anchored end by placing opposed notches therein which minimize discontinuities and hence impedance mismatch.

It is therefore an essential object of this invention to anchor a tapered arm in one end of a tube having two spaced coaxial cables at the other end to form a T, which arm makes contact to one of two center conductors in the coaxial cables; the arm is tapered so that the free end is smaller in cross section than the anchored end thereby providing a low distortion coaxial switch which is inexpensive to manufacture.

It is a further object of this invention to place at the anchored end of the arm opposed notches of small configuration to permit flexing of the arm with a minimum of discontinuities and signal distortion.

It is a further object of this invention to place a movable, concave plug axially aligned with the movable arm, which plug is axially movable to compensate for the characteristics of the arm to further minimize signal distortion.

These and other objects will become more apparent when a preferred embodiment is described in connection with the drawing in which:

FIGURE 1 is a sectioned view of a preferred embodiment of this invention;

FIGURE 2 is a plan view of the arm shown in FIG- URE 1;

FIGURE 3 is a plan view of the movable plug shown in the embodiment of FIGURE 1.

In FIGURE 1 is shown a tubular member 20 having spaced coaxial members 21, 22, at one end thereof. Located in each branch 21, 22 is a dielectric insert 23 and 24 respectively which carry centrally thereof center conductors 25 and 26 which have at their inner ends contacts 25a and 26a respectively, and which have spring fingers 25b and 26b respectively at their outer ends which are adapted for receiving the center conductors of coaxial cables.

At the other end of tube 20 is a coupling 29 in which is a dielectric insert 30 and anchored therein is an arm 31 which is tapered from the anchored end to a free end which is disposed between and aligned with contacts 25a and 26a. Arm 31 has contact surfaces 31a and 31b which register respectively with contacts 25a and 26a.

The purpose of the taper on arm 31 is to maintain a minimum distance between the sides of the arm and the inner walls of tube 20 whether the arm 31 is engaged with contact 25a or 26a. This is important since movement of arm 31 in tube 20 changes the capacitance therebetween. This capacitance change per arm position change varies logarithmically with the spacing between the arm and the inner wall, with the change being very large when the arm is close to the wall and with the change being smaller when the arm is nearer the center of tube 20. Hence, if the arm stays a predetermined distance away from the sides of the tube, then arm movement will not cause non-symmetrical troublesome capacitance changes. The predetermined distance depends on the characteristic impedance and the dielectric constant of the materials used in the switch.

In this embodiment, the inside diameter of the tube 20 is .144 inch and arm 31 is one inch long and is tapered from a .062 inch width to a .032 inch width before the additional taper for contact surfaces 31a, 31b.

Arm 31 is notched at the anchored end with fine slots 33 which permit the arm to flex and at the same time minimize signal distortion due to their configuration. In this embodiment the slots 33 are .006" in width and are .027 deep.

Means for moving arm 31 to contact 25a or 26a are electromagnets 35 and 35a each or" which has a coil 36 which is energized by a power source not shown. Mov able within coil 36 is a plunger 37 having a drive shaft 38 adjustably threaded therein. The inner end of drive shaft 38 carries a nylon pin 39 which passes through elliptical hole 40, which is .038 inch wide, in arm 31 and has a friction fit therewith so that movement of plunger 37 will cause movement of arm 31.

Situated at the left end of tube 20 is a plug 41 which is contoured on its inner side 41a (FIGURE 3) and is movable axially towards or away from the end of arm 31 to compensate for the particular impedance characteristics of the T junction in the switch to minimize signal distortion. Plug 41 is adjusted axially towards or away from arm 31 until the optimum signal transfer is accomplished and then is left in this set position.

Although this invention has been disclosed and illustrated with reference to particular applications, the principles involved are susceptible of numerous other applications which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

Having thus described my invention, I claim:

1. A coaxial cable switch comprising a tubular body of conductive material,

a dielectric insert being in one end of said tubular body,

a conductor arm in said tubular body being anchored at one end in said dielectric insert and having a free end movable from side to side in said body,

a pair of opposed coaxial lines extending on opposite sides of the free end of said arm whereby the free end of said arm is movable in one direction to contact the center condutcor of one of said coaxial lines and movable in the opposite direction to contact the center conductor of the other of said coaxial lines,

a plug contoured to the end of said arm,

said plug being in axial alignment with said arm and movable in an axial direction to vary the spacing between said plug and the free end of said arm to tune the conductive path for the signals flowing through said arm to said opposed coaxial lines.

2. A coaxial cable switch comprising a tubular body of conductive material,

a dielectric insert being in one end of said tubular body,

a conductor arm in said tubular body being anchored at one end in said dielectric insert and having a free end movable from side to side in said body,

said conductor arm having opposite sides thereof tapered toward said free end so that said free end is smaller in width than said anchored end,

a pair of opposed coaxial lines extending on opposite sides of the free end of said arm, with one coaxial line facing one tapered side and the other coaxial line facing the other tapered side,

said free end of said arm being movable in one direction so that one tapered side contacts the center conductor of one of said coaxial lines and movable in the opposite direction so that the other tapered side contacts the center conductor of the other of said coaxial lines, means to move said arm,

a plug contoured to the end of said arm in axial align- References Cited by the Examiner UNITED STATES PATENTS 2,472,274 6/49 Beleskas 3337 2,897,313 7/59 Burgess ZOO-153.18 2,951,925 9/60 Stewart ZOO-153.18

HERMAN KARL SAALBACH, Primary Examiner. 

1. A COAXIAL CABLE SWITCH COMPRISING A TUBULAR BODY OF CONDUCTIVE MATERIAL, A DIELECTRIC INSERT BEING IN ONE END OF SAID TUBULAR BODY, A CONDUCTOR ARM IN SAID TUBULAR BODY BEING ANCHORED AT ONE END IN SAID DIELECTRIC INSERT AND HAVING A FREE END MOVABLE FROM SIDE TO SIDE IN SAID BODY, A PAIR OF OPPOSED COAXIAL LINES EXTENDING ON OPPOSITE SIDES OF THE FREE END OF SAID ARM WHEREBY THE FREE END OF SAID ARM IS MOVABLE IN ONE DIRECTION TO CONTACT THE CENTER CONDUCTOR OF ONE OF SAID COAXIAL LINES AND MOVABLE IN THE OPPOSITE DIRECTION TO CONTACT THE CENTER CONDUCTOR TO THE END OF SAID ARM, A PLUG CONTOURED TO THE END OF SAID ARM, SAID PLUG BEING IN AXIAL ALIGNMENT WITH SAID ARM AND MOVABLE IN AN AXIAL DIRECTION TO VARY THE SPACING BETWEEN SAID PLUG AND THE FREE END OF SAID ARM TO TUNE THE CONDUCTIVE PATH FOR THE SIGNALS FLOWING THROUGH SAID ARM TO SAID OPPOSED COAXIAL LINES. 